1. Field of the Invention
This invention relates to a system for and method of treating a malfunctioning heart and, more particularly, to such a system and method which effects cardioversion/defibrillation in response to sensing a heart malfunction. The invention provides for the cardioverting/defibrillation of a malfunctioning heart as well as the possibility of overcoming a tachycardia manifestation without resorting to either cardioverting or defibrillating the heart.
2. Description of the Prior Art
In recent years, substantial progress has been made in pacemakers and in the development of cardioverting/defibrillating techniques for effectively treating various heart disorders and arrhythmias. Past efforts have resulted in the development of implantable electronic pacemakers and standby cardioverters-defibrillators which, in response to the detection of an abnormal cardiac rhythm, discharge sufficient energy via electrodes connected to the heart to depolarize and restore it to normal cardiac rhythm. An early example of this cardioverting/defibrillating technique is disclosed in U. S. Pat. No. 3,942,536 of Mirowski et al., the technique involving responses to a sensed peak right ventricular systolic pressure dropping to a fixed predetermined threshold level. This known technique did not involve mean pressure baselines, nor pressure changes in either direction therefrom.
Efforts have also been directed toward developing techniques for reliably monitoring heart activity in order to determine whether cardioversion/defibrillation are desirable or necessary. Such techniques include monitoring ventricular rate or determining the presence of fibrillation on the basis of a probability density function (PDF). A system using the PDF technique statistically compares the location of points of a cardiac waveform with the expected locations of points of the normal waveform. When the waveform becomes irregular, as measured by its probability density function, an abnormal cardiac function is suggested. The latter technique is described in U.S. Pat. Nos. 4,184,493 and 4,202,340 both of Langer et al.
A more recent system, as disclosed in U. S. Pat. No. 4,475,551 of Langer et al. utilizes both the PDF technique to determine the presence of an abnormal cardiac rhythm and a heart rate sensing circuit for distinguishing between ventricular fibrillation and high rate tachycardia (the latter being indicated by a heart rate above a predetermined minimum threshold), on the one hand, and normal sinus rhythm or a low rate tachycardia (indicated by a heart rate falling below a pre-determined minimum threshold), on the other hand.
Still further, research in this area has resulted in the development of a heart rate detector system which accurately measures heart rate from a variety of different electrocardiogram (ECG) signal shapes. One such system is disclosed in U.S. Pat. No. 4,393,877 of Imran et al.
Despite these past efforts and the level of achievement prevalent among prior art systems, there are potential difficulties and drawbacks which may be experienced with such devices.
Currently antitachycardia systems detect arrhythmias primarily by sensing rate and perform inadequately in the differentiation of hemodynamically stable from unstable rhythms. These devices, for example, may fire during a stable supraventricular tachycardia (SVT) inflicting pain and wasting energy; damage to the heart may result.
A commonly used implantable antitachycardia device is the automatic implantable cardioverter-defibrillators (AICD) which is commercially available under the model designations 1500, 1510 and 1520 from Cardiac Pacemakers, Inc. whose address is: 4100 North Hamlin Avenue, St. Paul, Minn. 55164. These devices continuously monitor myocardial electrical activity, detecting ventricular tachycardia (VT) and ventricular fibrillation (VF), and delivering a shock to the myocardium to terminate the arrhythmia. The AICD has been shown to reduce the mortality rate in patients with malignant arrhythmias with initial studies at Johns Hopkins Hospital and Stanford Medical Center demonstrating a 50 percent decrease in the anticipated total incidence of death, as reported by Mirowski et al., "Recent Clinical Experience with the Automatic Implantable Cardioverter-Defibrillator", Medical Instrumentation, Vol. 20, pages 285-291 (1986). Arrhythmias are detected by (1) a rate (R wave) sensor and (2) a probability density function (PDF) which defines the fraction of time spent by the differentiated electrocardiogram between two amplitude limits located near zero potential. Presently, the functional window of the PDF is wide to permit the detection of both VT and VF, and therefore, this device functions essentially as a rate-only sensing system. As reported by Mirowski, "The Automatic Implantable Cardioverter-Defibrillator: An Overview", JACC, Vol. 6, No. 2, pages 461-466, (August, 1985), when an arrhythmia fulfills either the rate or PDF criteria, the device delivers Schuder's truncated exponential pulse of 25 Joules some 17 seconds after the onset of the arrhythmia. The device can recycle as many as three times if the previous discharge is ineffective with the strength of the second, third and fourth pulses being increased to 30 Joules. After the fourth discharge, approximately 35 seconds of nonfibrillating rhythm are required to reset the device.
The Mirowski et al., supra, and the Mirowski, supra publications set out, in summary form, background material relating to the defibrillating/cardioverting arts against which the present invention was made.
In addition to the standard automatic implantable cardioverter-defibrillator characterized by the above-noted, dual detection algorithm, a variant of the device which features a sensing system that relies only on the analysis of heart rate is also available. This "rate-only" version of the known cardioverter-defibrillator preferred by some investigators, is more sensitive than the dual detection version unit and theoretically less likely to miss ventricular tachycardias with narrow QRS complexes. It is believed that the "rate-only" system, on the other hand, may be too sensitive, delivering cardioverting/defibrillating pulses too often or too soon, no hemodynamic parameter having been taken into consideration.
One problem with current systems is that they function primarily as a rate-only sensing systems and may fire for nonmalignant as well as malignant tachycardias. These firings are not benign; potentially endangering myocardium, wasting energy and inflicting pain on the conscious patient, all distinct shortcomings and disadvantages.
The principal object of the present invention is to provide a system for cardioverting/defibrillating which avoids unnecessary firings, thereby reducing the danger to the myocardium, saving energy and avoiding pain.
Another object of the present invention is to provide an implantable system for cardioverting/defibrillating which avoids unnecessary firings, thereby reducing the danger to the myocardium, saving energy and avoiding pain.
A further object of the present invention is to provide a system for cardioverting/defibrillating which is hemodynamically responsive to change in pressure from baseline mean pressure.
An additional object of the present invention is to provide a system for cardioverting/defibrillating which is hemodynamically responsive to change in baseline mean pressure and to rate criteria.
Yet another object of the present invention is to provide a method of cardioverting/defibrillating which may be advantageously carried out using a cardioverter-defibrillator constructed in accordance with the present invention.
Yet a further object of the present invention is to provide a method of cardioverting/defibrillating which avoids unnecessary firings thereby reducing the danger to the myocardium, saving energy and avoiding pain.
In accordance with preferred embodiments of the present invention, new sensing algorithms are proposed using hemodynamic or both hemodynamic and rate criteria, the latter being taken in series or parallel. The series configuration algorithm could be effected by detecting rate with an intracardiac, extracardiac, or body-surface R-wave sensor. When rate exceeds the programmed cut-off value, at least one hemodynamic parameter, such as departures from baseline mean right atrial pressure (MRAP), mean right ventricular pressure (MRVP), mean central venous pressure (MCVP) or mean arterial pressure (MAP) would be monitored. Mean left atrial pressure (MLAP) or mean left ventricular pressure (MLVP) may also be suitable as one or another of the hemodynamic baseline parameters from which changes may be monitored. If mean right arterial pressure (MRAP) or mean right ventricular pressure (MRVP) or mean central venous pressure (MCVP) increases from respective baseline MRAP or MRVP or MCVP baselines within a time period of predetermined duration, indicating hemodynamic compromise, the system would fire. If mean left atrial pressure (MLAP) or mean left ventricular pressure (MLVP) increases respectively from respective baseline MLAP or baseline MLVP within a time period of predetermined duration indicating hemodynamic compromise, the system would fire. If mean arterial pressure (MAP) decreases from baseline MAP beyond a predetermined magnitude indicating hemodynamic compromise the system would fire. If the respective pressure changes were less than the respective predetermined magnitudes, pressures would be monitored to determine if respective changes from the respective mean levels take place, as long as the rate criteria is satisfied. A parallel configuration algorithm in which rate and hemodynamic criteria function simultaneously is also proposed; however, continuous pressure change determination would probably be less energy efficient. Either configuration of algorithm could be adapted to a single catheter consisting of a pressure transducer in either the right atrium or right ventricle and an R-wave sensing electrode or pair of electrodes at the catheter tip in the right ventricle. The hemodynamic information derived from an arterial line, Swan-Ganz catheter (already present in the intensive/cardiac care unit patients), or even an automated mechanical blood pressure cuff could be integrated together with the electrocardiogram to provide a temporary automatic antitachycardia system. Cardioversion-defibrillation could be administered using externally applied patches. Even a noninvasive hemodynamically responsive antitachycardia system is potentially feasible using doppler technology for pressure measurements. The PDF (narrow window of function) and the rate/pressure sensing algorithm could be used simultaneously such that if the rate/pressure criteria are satisfied (indicating hemodynamically significant SVT or VT) the device cardioverters and if the PDF criteria is satisfied indicating (VF) defibrillation results. This pulse delivery system could also be incorporated into a single catheter.
It is to be appreciated that when the pressure criteria is not met, but the rate criteria indicates tachycardia is present, an antitachycardia pacemaker could be enabled in an effort to correct the malfunction.
MAP is an excellent parameter but accurate continuous measurement requires an indwelling arterial catheter or transducer which over time is prone to infection and thrombus formation (with the potential for systemic embolic events). MRAP and MRVP appear to relate useful information regarding the hemodynamic state of the particular arrhythmia. If tricuspid stenosis were present, MRVP would probably be more reliable than MRAP. Preliminary observations in the canine model suggest that changes as small as 3 mmHg for MRAP and MRVP and as small as 15 mmHg for MAP are significant and can be used in carrying out the present invention.
The rate/pressure sensing algorithms could also help integrate a cardioverter-defibrillator with an antitachycardia pacemaker. The hemodynamic function would determine which of these devices to engage. For example, when a hemodynamically significant tachycardia is detected the cardioverter-defibrillator would be used to terminate the arrhythmia. When a hemodynamically stable tachycardia is sensed the antitachycardia pacemaker would attempt to terminate the arrhythmia using such methods as overdrive, burst, or extra stimulus pacing, incremental or decremental scanning, or ultra-high frequency stimulation. If the tachycardia was accelerated, this would be detected by the rate/pressure sensing algorithm and cardioverted or defibrillated. With a pacemaker present, a bradycardia failsafe could be built into the system.
The adaptation of a hemodynamic parameter to the sensing system of antitachycardia devices appears to be a logical improvement to its present function. MRAP and MRVP are easily measured parameters (via the transvenous route) and appear to relate important hemodynamic information. MAP is an easily measured parameter in the intensive/cardiac care unit setting and could be integrated together with the electrocardiogram to form a temporary automatic antitachycardia system. A rate/pressure sensing algorithm, designed either in series or parallel, could be integrated with the PDF system such that hemodynamically significant SVT, VT, and VF would be detected. The rate/pressure sensing algorithm could also be applied to a combined cardioverter-defibrillator and antitachycardia pacemaker.
The present invention, from one vantage point, can be viewed as a system for treating a malfunctioning heart, the system including storage means for storing electrical energy. Pressure responsive sensing means is provided for sensing at least one hemodynamic parameter. Electrode means are utilized for electrically coupling the storage means to the heart. Means responsive to output from the sensing means charge and enable discharge of the electrical energy stored by the storage means across the electrode means and into the heart upon sensing a change in pressure of a predetermined amount from mean baseline pressure.
From a somewhat different vantage point, the invention can be seen as being a system for treating a malfunctioning heart, the system including means for sensing heart rate and producing a first control signal whenever the rate exceeds a predetermined rate. Pressure responsive means are provided for sensing at least one hemodynamic parameter and for producing a second control signal whenever the sensed hemodynamic parameter departs from mean baseline pressure by at least a predetermined amount. Controllable antitachycardia pacemaking means is provided to supply pacing signals to the heart, if needed. Controllable cardioverting/defibrillating means including storage means for storing electrical energy and electrode means are provided to apply electrical energy from the storage means to the heart to cardiovert or to defibrillate same, if needed. Control circuit means respond to the first control signal and to the second control signal for enabling the antitachycardia pacemaking means whenever both the first control signal is present and the second control signal is absent and for enabling said cardioverting/defibrillating means whenever the first control signal and the second control signal are present. Means are arranged to discharge the electrical energy stored by the storage means across the electrode means and into the heart.
The pressure responsive sensing means for sensing at least one hemodynamic parameter may include signal processing means for determining mean right atrial pressure (MRAP), mean right ventricular pressure (MRVP), mean central venous pressure (MCVP), mean left atrial pressure (MLAP), mean left ventricle pressure (MLVP) or mean arterial pressure (MAP) may be provided.
The signal processing means for determining mean pressure may include means for providing a control signal whenever the mean pressure departs from mean baseline pressure by at least a predetermined amount. The means responsive to output from the sensing means for charging and enabling discharge is coupled to the signal processing means and is responsive to the output control signal.
The signal processing means for determining mean pressure may include means for providing an output control signal whenever the current mean pressure or instant pressure increases, in all but the case in which arterial pressure is involved, a predetermined amount from baseline mean pressure. The means responsive to output from the sensing means for charging and enabling discharge is coupled to the signal processing means and is responsive to the control signal.
In those cases where the pressure responsive sensing means for sensing at least one hemodynamic parameter includes signal processing means for determining baseline mean arterial pressure, departures in current mean pressure or instant pressure from the mean baseline pressure is in a decreasing direction.
The system may include a microprocessor for developing control signals to control the application of electrical energy to the heart, as well as controlling an antitachycardia pacemaker.
From a slightly different vantage point, the invention can be seen as a system for treating a malfunctioning heart, the system including means for providing cardioverting/defibrillating electrical energy and pressure responsive sensing means for sensing at least one hemodynamic parameter. Means responding to output from the sensing means deliver the cardioverting/defibrillating electrical energy into the heart upon sensing a change in instant pressure or current mean pressure of a predetermined magnitude from mean baseline pressure.
The invention can also be seen as a system for treating a malfunctioning heart, the system including means for sensing heart rate and producing a first control signal whenever the rate exceeds a predetermined rate. Pressure responsive means is provided for sensing at least one hemodynamic parameter and for producing a second control signal whenever the sensed hemodynamic parameter departs from mean baseline pressure by at least a predetermined amount. Controllable antitachycardia pacemaking means is provided to supply pacing signals to the heart. Controllable cardioverting/defibrillating means produce cardioverting/defibrillating electrical energy. Control circuit means, respond to the first control signal and to the second control signal and enable the antitachycardia pacemaking means whenever both the first control signal is present and the second control signal is absent. The control circuit means enable the cardioverting/defibrillating means whenever the first control signal and the second control signal are present.
The invention can be viewed as being in a system for treating a patient having a malfunctioning heart which includes means responsive to at least one control signal for supplying the patient with malfunction-correcting input. The system is improved by pressure responsive means for sensing at least one hemodynamic pressure parameter. The control signal is produced upon sensing a change in pressure of a predetermined amcunt from mean baseline pressure. The input may be electrical signals and/or electrical energy delivered to the malfunctioning heart.
The invention is, from another vantage point, a system for treating a patient having a malfunctioning heart which includes means responsive to at least two control signals for supplying the patient with malfunction-correcting input. Pressure responsive means are provided for sensing at least one hemodynamic pressure parameter to produce one of the two control signals upon sensing a change in pressure of a predetermined amount from mean baseline pressure. Means responsive to heart rate produce the second of the two control signals. The input may be electrical signals and/or electrical energy delivered to the malfunctioning heart.
In its method aspect, the invention may be viewed as a method of treating a malfunctioning heart, the method including the step of sensing at least one parameter of heart activity. In accordance with a salient feature of the invention, the improvement includes sensing change in at least one hemodynamic pressure parameter from a mean baseline pressure, and thereafter delivering cardioverting/defibrillating electrical energy to the heart in response at least to change of predetermined magnitude in the sensed hemodynamic pressure parameter from the mean baseline pressure. Thus, a malfunction susceptible to correction by delivering electrical energy to the heart is corrected.
The step of sensing change in at least one hemodynamic parameter may include determining change in or from mean baseline right atrial pressure (MRAP), mean baseline right ventricle pressure (MRVP), mean baseline central venous pressure (MCVP), mean baseline left atrial pressure (MLAP) or mean baseline left ventricular pressure (MLVP) in an increasing direction, and, if desired, sensing heart rate, the step of delivering cardioverting/defibrillating electrical energy being taken only when the heart rate (if this be a selected criteria) exceeds a given rate and/or the change in or from mean baseline pressure exceeds the predetermined magnitude. If the heart rate is not a selected criteria, the step of delivering the electrical energy would be taken when the change in pressure from mean baseline pressure has been sensed, regardless of the heart rate.
The step of sensing change in at least one hemodynamic parameter may include determining change in or from mean baseline arterial pressure in a decreasing direction. The step of sensing the heart rate could be used, in the case of arterial pressure change, as an additional criteria.
In its method aspect the invention can be seen as being in an improvement in a method of treating a patient having a malfunctioning heart, which includes sensing change in at least one hemodynamic pressure parameter from a mean baseline pressure; and delivering to the patient malfunction-correcting input in response at least to change of predetermined magnitude in the sensed hemodynamic pressure parameter from the mean baseline pressure. This improved method may include sensing heart rate, the step of delivering to the patient being taken when the heart rate exceeds a given rate and the change in mean pressure from mean baseline pressure exceeds the predetermined magnitude. The step of delivering input to the patient may involve delivering electrical signals and/or electrical energy to the malfunctioning heart.
The novel features that are considered characteristic of the invention in its method and system aspects are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with other objects and advantages thereof is to be understood from the following description of illustrative embodiments, when read in conjunction with the accompanying drawings, wherein like reference numerals refer to like components.